The Akismet blog announced this morning that Akismet accounts will now require a WordPress.com sign-in. They already required an Akismet login, but now it's integrated directly with WordPress.com. There are some checks Akistmet is doing for people that didn't have .com accounts. But new accounts will all require WordPress.com logins. Akismet is still bundled with WordPress core too, and to my knowledge, tickets requesting that it be unbundled haven't made much progress.